In the cation of the title salt, C11H17N2O+·C7H8ClN2O2−, the piperazine ring adopts a distorted chair conformation and contains a positively charged N atom with quaternary character. Its mean plane makes a dihedral angle of 42.36 (8)° with the phenyl ring of its 2-methoxyphenyl substituent. The 2,4-dioxopyrimidin-1-ide anion is generated by deprotonation of the N atom at the 1-position of the pyrimidinedione ring. Intramolecular C—H⋯O hydrogen bonds generate S(6) ring motifs in both the cation and the anion. In the crystal, N—H⋯O, N—H⋯N and C—H⋯O hydrogen bonds are also observed, resulting in a two-dimensional network parallel to the ab plane. The crystal stability is further consolidated by weak C—H⋯π interactions.